1. Field of the Invention
The present invention relates to a diode and a fabricating method thereof, and particularly to a light emitting diode (LED) and a fabricating method thereof.
2. Description of Related Art
The group IIIA nitrides have broader energy gaps, therefore LEDs made of such can emit lights of a large band range from ultraviolet band to red light band which almost covers all of the visible band. Nowadays, the use of the group IIIA nitride semiconductors including GaN, AlGaN, InGaN becomes more and more attractive. Comparing to conventional light bulbs, such LEDs have outstanding advantages including smaller volume, longer lifetime, lower driving voltage, invulnerableness, less contamination and higher light emitting efficiency; therefore, LEDs are more and more widely used in commerce.
Referring to FIG. 1, a schematic cross-sectional view of a conventional LED is illustrated. The conventional LED 100 includes an Al2O3 substrate 110, an epitaxy buffer layer 120, a doped semiconductor layer 132, a light emitting layer 134 and a doped semiconductor layer 136. The epitaxy buffer layer 120 is disposed on the Al2O3 substrate 110, and the doped semiconductor layer 132 is disposed on the epitaxy buffer layer 120. The light emitting layer 134 is disposed on a part of the doped semiconductor layer 132, and the doped semiconductor layer 136 is disposed on the light emitting layer 134. It is to be noted that the doped semiconductor layer 132 and the doped semiconductor layer 136 are different types. For example, the doped semiconductor layer 132 is a P-type doped semiconductor layer, while the doped semiconductor layer 136 is an N-type doped semiconductor layer.
Furthermore, a portion of the doped semiconductor layer 132 will be exposed after an etching process. Therefore, the conventional LED 100 further includes a pair of pads 142 and 144 respectively disposed on and electrically connected with the exposed portion of the doped semiconductor layer 132 and the doped semiconductor layer 136. An ohmic contacting layer 152 is disposed between the pad 142 and the doped semiconductor layer 136, and another second ohmic contacting layer 154 is disposed between the pad 144 and the doped semiconductor layer 132. It should be noted that the conventional LED 100 is usually electrically connected with the circuit board or other carriers (not shown) by wire bonding technology or flip chip technology, wherein the pads 142 and 144 are the contacting points for electrically connection.
In the foregoing LED 100, the Al2O3 substrate 110 has poor heat dissipation. Therefore, after a long time of light emission, the temperature of the light emitting layer 134 will increase and the light emitting efficiency of which will decrease accordingly. Furthermore, the pad 142 shelters a part of emitted light and consequently affect the light emitting efficiency, while disposing the pads 144 also reduces a part of light emitting area. Moreover, because a current crowding effect occurs at the pads 142 and 144, which causes excessive current thereby, the doped semiconductor layer 132 and the doped semiconductor layer 136 will be damaged at the portions near the pads 142 and 144. As a result, the LED 100 can not function properly.
FIG. 2A is a schematic cross-sectional view of another conventional LED. Referring to FIG. 2A, the conventional LED 200a includes a transferring substrate 210a, a bonding layer 220a, a doped semiconductor layer 232a, a light emitting layer 234a and a doped semiconductor layer 236a. The bonding layer 220a is disposed on the transferring substrate 210a, and the doped semiconductor layer 232a is disposed on the bonding layer 220a. The light emitting layer 234a is disposed between the doped semiconductor layer 232a and the doped semiconductor layer 236a. It is to be noted that the doped semiconductor layer 232a, the light emitting layer 234a and the doped semiconductor layer 236a are originally formed on a same epitaxy substrate (not shown). They are consequentially transferred to the transferring substrate 210a, while the bonding layer 220a is adapted for sticking the transferring substrate 210a and the doped semiconductor layer 232a. 
Similarly, a pad 242a is usually disposed on the doped semiconductor layer 236a, and an ohmic contacting layer 252a is disposed between the pad 242a and the second doped second semiconductor layer 236a. The pad 242a has the same utility and function of the pads 142 and 144 in FIG. 1. Herein, the transferring substrate 210a and the bonding layer 220a are electrically conductive. Therefore, when the conventional LED 200a is disposed on a circuit board or other carriers, it can be electrically connected with the circuit board via the transferring substrate 210a directly and electrically connected with the circuit board via a conducting wire (not shown) bonding on the pad 242a. However, such a conventional LED 200a requires a relatively high driving voltage.
FIG. 2B is a schematic cross-sectional view of another conventional LED. Referring to FIG. 2B, the conventional LED 200b includes a transferring substrate 210b, a bonding layer 220b, a doped semiconductor layer 232b, a light emitting layer 234b and a doped semiconductor layer 236b. The bonding layer 220b is disposed on the transferring substrate 210b, and the doped semiconductor layer 232b is disposed on the bonding layer 220b. The light emitting layer 234b is disposed on a part of the doped semiconductor layer 232b, and the doped semiconductor layer 236b is disposed on the light emitting layer 234b. Pads 242b and 244b are respectively disposed on the doped semiconductor layer 236b and the exposed doped semiconductor layer 232b after an etching process. Furthermore, the transferring substrate 210b is made of semiconductor materials or nonconductive materials.
It is to be noted that ohmic contacting layers 250b and 252b are employed between the pads 244b, 242b and the doped semiconductor layers 232b, 236b for improving the interface properties therebetween. However, employing extra ohmic contacting layers means extra fabrication cost and extra processing.